You should have your frost dk go 2h haste (I think) to abuse that +50% melee damage buff, and have him solo strengths. Rogue mage ele shammy full time on rages, and hunter and either mage and ele shammy help out on courages. The disc priest should go shadow, and just run dots on the strengths, two bosses, and the rages.
For soaking, you're pretty set with a dispersion, 1min detter, and rogue soaks, plus you can throw in 2 min defensive CDs with your other classes.
Only tips I can tell you is that your hunter should pick up spirit bond and Crouching Tiger, and your rogue should pick up elusiveness.

As for having a melee on the bosses i wouldn't recommend it, this fight is mostly about controlling the adds. Tanks damage and the dead time between waves should be more than enough to kill them really.

Warlocks= soak every courage spark
Rogue= every rage spark ...Feint and a power word shield he might only even need to be topped off tbh
Shadowpriest= soaks rage set
Hunter soaks =rage set
resto druid with symbyosis deterrence=rage soak
boomkin with cloak of shadows= another rage soak
Your mage would also be your emergency soak 1 with cauterize for a single spark and can soak 2 with block if timed correctly
dk can also emergency soak a single spark with all cd's up.

Also with the way gear is now you can kill any spark set you choose to they die fairly quickly so if someone is late on a soak or fucks up or w/e the case may be you can just kill the sparks as long as they are snared so you aren't kiting them.

My thoughts were that we would have the priest go shadow and have the rogue tanking strength. Is it recommended to have a melee sit on boss and dance? Any strats and or tips would be helpful. Thanks!

Our setup for this has always been the following:

Tanks:

Brewmaster monk
Blood DK

Healers:

Holy paladin
Restoration druid

DPS:

Shadow priest (mainspec holy/disc, usually soaks sparks from courages except the first one)
Mage
Warlock
Warrior ("tanking" strenghts, only assisted by ranged if needed)
Elemental shaman
Rogue (That's me and my sole purpose for the fight is to solo-soak the sparks along with supporting with damage and CC on rages)

Shortly, I as a rogue soak every spark except for courages after bosses have jumped down. If there is more than one spark and they're close to each other, I will go for them with cloak of shadows. Just feint soaking (Elusiveness-talent is strongly suggested) otherwise. We have our holy paladin/mage/warlock to assist with soaking if the sparks are spread around the room but I can usually just sprint/nitro/shadowstep everywhere.

Rogue soaking may be hard to nearly impossible depending on his gear (and thus healthpool), but it's definately worth the shot since if you can afford to keep one healer healing the raid and the rogue, soaking sparks will become very easy. As I mentioned, Elusiveness is required if you let your rogue soak them all.

It's quite messy at first, hopefully I were able to help out at all. Good luck and have fun!